ABSTRACT
A separator modification strategy was proposed by placing nitrogen-doped carbon fibers (NCF700) in the middle of the separator to prevent direct contact between the coating and the rigid zinc metal anode, resulting in coating cracks. The NCF700 coating can homogenize the electric field distribution and increase the transference number of zinc ions. Therefore, the battery assembled with the NCF700 coated separator exhibits superior cycling stability compared to the bare separator.
ABSTRACT
The serpentine germanate materials are promising oxygen evolution reaction (OER) electrocatalysts due to their unique layered crystal structure and electronic structure. However, the catalytic activities still need to be improved to satisfy the practical applications. Adjusting the d-band center of metal active site to balance the adsorption and desorption of intermediates is considered an effective approach to improve the OER activity. In this work, an element dopant strategy was proposed to optimize the d-band state of Ni3Ge2O5(OH)4 serpentine to improve the OER activity. The density functional theory calculations revealed that Fe3+ doping increased the d-band center of the Ni3Ge2O5(OH)4 serpentine, which optimized the adsorption strength of intermediates on surface Ni and Fe atoms so that the Fe3+ doped Ni3Ge2O5(OH)4 (Ni2.25Fe0.75Ge2O5(OH)4) exhibited much reduced Gibbs free energy changes in the rate-determining step compared with pristine serpentine. Inspired by the theoretical calculations, the NixFe3-xGe2O5(OH)4 nanosheets with different amounts of doped Fe3+ were designed and synthesized. The structural characterizations indicated that Fe3+ was successfully doped into Ni3Ge2O5(OH)4 and replaced the Ni2+. The Fe3+ doped NixFe3-xGe2O5(OH)4 nanosheets showed greatly improved OER activity than Ni3Ge2O5(OH)4 and Fe3Ge2O5(OH)4. Further electrochemical analysis illustrated that Fe3+ doping reduced the adsorptive/formative resistance of intermediates and the charge transfer resistance and facilitated the kinetic process of OER. The in situ Raman spectra indicated that the Fe3+ doped Ni3Ge2O5(OH)4 possesses a more active Ni-O bond than pristine Ni3Ge2O5(OH)4. This work provides an effective strategy to tune the d-band center of serpentines for efficient electrocatalytic OER.
ABSTRACT
As green and sustainable methods to produce hydrogen energy, photocatalytic and electrochemical water splitting have been widely studied. In order to find efficient photocatalysts and electrocatalysts, materials with various composition, size, and surface/interface are investigated. In recent years, constructing suitable nanoscale hetero-interfaces can not only overcome the disadvantages of the single-phase material, but also possibly provide new functionalities. In this review, we systematically introduce the fundamental understanding and experimental progress in nanoscale hetero-interface engineering to design and fabricate photocatalytic and electrocatalytic materials for water splitting. The basic principles of photo-/electro-catalytic water splitting and the fundamentals of nanoscale hetero-interfaces are briefly introduced. The intrinsic behaviors of nanoscale hetero-interfaces on electrocatalysts and photocatalysts are summarized, which are the electronic structure modulation, space charge separation, charge/electron/mass transfer, support effect, defect effect, and synergistic effect. By highlighting the main characteristics of hetero-interfaces, the main roles of hetero-interfaces for electrocatalytic and photocatalytic water splitting are discussed, including excellent electronic structure, efficient charge separation, lower reaction energy barriers, faster charge/electron/mass transfer, more active sites, higher conductivity, and higher stability on hetero-interfaces. Following above analysis, the developments of electrocatalysts and photocatalysts with hetero-structures are systematically reviewed.
